1. Technical Field
The present invention generally relates to a crystal fiber and, more particularly, to a sapphire crystal fiber doped with two transition metals having different concentrations so as to generate a wide-band light beam and a narrow-hand light beam for use in a Raman spectrometer.
2. Description of the Prior Art
Raman effect refers to inelastic scattering of a photon interacting with substances. Raman spectroscopy reveals the shift in the scattered photon frequency away from the incident photon frequency, also known as Raman shift, which has been widely used in detections and analyses in chemistry, bio-technology and medical science because molecular identification can be achieved according to vibrational spectroscopic information of chemical bonds and symmetry of molecules.
Generally, only one in every 106 to 108 photons is inelastically scattered, which leads to difficulty in detection of inelastically scattered photons. Therefore, inspection light source with a higher power, for example higher than 150 mW, is preferably adopted to project on the specimen in order to make detection less difficult. However, the inspection light with such a high power may induce undesirable damages to human bodies or other biological samples when Raman spectroscopy is applied. In addition, such condition may violate related medical laws and regulations.
To facilitate Raman spectroscopy, the power of inelastically scattered photons can be enhanced by determining the wavelength of the inspection light so that the wavelength falls within an absorption band of the specimen. However, to detect a wide variety of specimens, devices for generating inspection light are required to be capable of wavelength tuning during Raman spectroscopy measurement. In most cases, Raman spectroscopy requires that the detection light projects on the specimen for a long time, which results in low throughput as well as possible damages to the specimen. Moreover, the devices for generating inspection light may enlarge the size and add manufacturing cost to the Raman spectrometer when it provides wavelength tuning.